Electric motors, gear boxes, and rolling mills are common work machines having a housing with a rotatable shaft for use in performing work. The shaft is normally journaled within a bearing mounted in the housing. The bearing and shaft are normally lubricated with oil, grease or the like.
The importance of maintaining the lubricating fluid within the housing and of preventing contaminants from entering the housing are well known. Loss of lubricant or contamination of the lubricant with foreign matter, including moisture, will cause premature bearing failure.
While lip and labyrinth seals are historically the primary type of seals used to retain the lubricant within the housing while withholding contaminates, more recently, improved seals have been developed which greatly improve the life of the bearing. For example, applicant's prior U.S. Pat. No. 4,022,479 discloses a seal comprising a stator ring fixed to the housing and a rotor ring sealingly mounted on the shaft for rotation therewith. As described in the '479 patent, the stator has a series of labyrinth grooves for collecting any migrating lubricant, and has a trough or drain which returns lubricant from the groove to the housing sump. Contaminants entering the seal between the stator and rotor rings are collected in a channel or channels and expelled through a port to the exterior of the housing.
Applicant has improved and modified the basic sealing structure disclosed in the '479 patent, with such modifications being disclosed in U.S. Pat. No. 4,114,902, 4,175,752, 4,304,409, 4,466,620, 4,706,968 and 4,832,350.
Even with the improved labyrinth-type seals developed by applicant, problems of lubricant migration and welling exist in some environments, such as with sleeve bearing electric motors, gear boxes, and rolling mills, each of which present special sealing problems. Such migration and welling of the lubricant occur due to the high axial velocity at which the lubricant is impinged upon the bearing and shaft. These problems also exist, though to a lesser extent, when the bearing is ring-oiled. Also, the lubricant tends to migrate along the shaft and pass out of the housing due to the pressure differential caused by the air flow velocity, and the resulting energy, existing between the housing sump and the atmosphere.
For example, electric motors normally utilize air flow to cool the bearings and motor. However, such air flow creates a relative vacuum in the sump, and thus a pressure differential which may cause lubricant to leak out of the motor housing. Also, the shaft of an electric motor may shift axially between a mechanical center when the motor is at rest and a magnetic center when the motor is in operation. Such shifting of the shaft may displace the conventional seal or bearing isolator, thereby allowing further leakage of lubricants and/or lubricant contamination.
As another example, a gear box, or speed reduction gearing, has bearings which are subjected to a deluge of high velocity lubricant. The lubricant level within the sump often rises above the shaft OD, so as to overcome the gravity drainage system of lubricant back into the sump. Lubricant leakage is often present due to the excess lubricant. Also, oil lubrication used in gear boxes is often a foaming variety, which increases the volume and height above the shaft OD so as to cause further leakage.
A rolling mill is another example of a machine which may be subject to premature bearing failure. The rolls are changed or replaced frequently. As is often the case, the roll shaft seals may be damaged. Such shaft seal damage may allow kerosene or other lubricant used at the nip or contact point of the material to flow into and destroy the bearing at each end of the roll. Also, undesirable leakage of bearing lubricant onto the rolls may occur. This is particularly detrimental when the material being processed is food which then becomes contaminated.
The seal of the present invention, while useful on most work machines that use rotating shafts, is especially designed to meet the specific problems of electric motors, gear boxes and rolling mills.
One primary objective of the invention is the development of an improved seal which may be used to overcome the problems discussed above with regard to electric motors, gear boxes and rolling mills.
Another primary objective of the present invention is the provision of an improved seal to overcome migration and welling problems in equipment having lubricated rotating shafts.
Another objective of the present invention is the provision of an improved seal which exerts energy on the lubricant entering the seal so as to counter the energy resulting from the internal and external pressure differential and the impingement velocity of the lubricant.
Still another objective of the present invention is the provision of a sealing structure having a captured rotor that is mounted within the stator so as to prevent the axial and radial displacement of said rotor.
These and other objectives will become apparent from the description of the invention.